Aluminium chloride in acidified aqueous solution forms an ion having geometry

We need to determine the geometry of the ion formed when aluminium chloride is dissolved in acidified aqueous solution.

Key Concept: When $$AlCl_3$$ dissolves in acidified aqueous solution, the $$Al^{3+}$$ ion is strongly hydrated by water molecules due to its high charge density.

In aqueous solution, $$AlCl_3$$ dissociates: $$AlCl_3 \rightarrow Al^{3+} + 3Cl^-$$

The $$Al^{3+}$$ ion, being small and highly charged, coordinates with six water molecules to form the hexaaquaaluminium(III) ion: $$Al^{3+} + 6H_2O \rightarrow [Al(H_2O)_6]^{3+}$$

In the complex $$[Al(H_2O)_6]^{3+}$$, the coordination number of aluminium is 6. With 6 ligands around the central metal ion, the geometry is octahedral.

$$Al^{3+}$$ has the electronic configuration $$[Ne]$$ (or $$1s^2 2s^2 2p^6$$), which has no d-electrons. With sp^3d^2 hybridisation, six water molecules arrange themselves in an octahedral geometry around $$Al^{3+}$$.

Answer: Option 1 — Octahedral